The intestinal mucosa is a major route of infection of the human immunodeficiency virus. In addition, some of the most severe manifestations of the acquired immunodeficiency disease syndrome (AIDS) involve the gastrointestinal tracts. In particular, patients with AIDS frequently suffer from diarrhea in which there is no identifiable infectious agent, and from chronic cachexia. The proposed studies will investigate the human intestinal epithelial cell as a host cell type for HIV infection. The project involves a close collaboration between laboratories with combined expertise in immunology and molecular biology. The research is divided into 4 interrelated experimental studies: 1) studies of the infectivity of HIV for human intestinal epithelial cells. The well- differentiated human colon cancer cell line T84 will serve as a model to study factors that influence HIV intestinal infection in vitro. 2) Studies of in vivo infection of the human intestinal epithelium by HIV. In these studies, colon and small intestinal biopsies from normal controls, patients with AIDS related complex (ARC), and AIDS patients will be studied using in situ hybridization to detect HIV gene transcripts and CD4 mRNA in epithelial cells and, by immunohistochemistry to detect the expression of HIV gene products and the CD4 molecule. 3) studies of the regulation of HIV gene expression using recombinant DNA plasmids containing the regulatory regions of the HIV genome. These constructs will be transciently introduced into the T84 cells to assess the regulation of their expression. 4) Studies of physiologic changes in the T84 cells upon infection with HIV. These experiments will measure vectoral ion transport and resistance across T84 cell line monolayers in Ussing chambers. The above experimental approach will provide new insights into the role of intestinal epithelial cells in HIV infection and the effect of HIV infection on intestinal physiology.